The present invention relates to a flat type cathode ray tube for use in a color television receiver set or a computer terminal display.
A prior art flat type cathode ray tube includes a phosphor plane arranged on an inner surface of a vacuum enclosure, a plurality of vertical deflection electrodes arranged in parallel and facing relation to the phosphor plane and vertically divided at a predetermined pitch, and horizontally extending electron guns arranged in a direction of vertical scanning on the phosphor plane to emit electron beams. Each electron gun comprises a thermal electron source for generating thermal electrons, a grid electrode for generating thermal electrons as electron beams corresponding to horizontally arranged pixels and modulation electrodes for modulating respective beams in accordance with a picture signal. The electron beams modulated corresponding to the horizontally arranged pixels are directed to a space between the phosphor plane and the vertical deflection electrode and a deflection voltage to the vertical deflection electrode is sequentially changed so that the phosphor plane is vertically scanned by the electron beams.
In such a flat type cathode ray tube, the electron gun for generating the electron beams should generate electron beams one for each of the horizontally arranged pixels. Since one pixel in a conventional color television image has a size of 0.1-0.2 mm, it is difficult from electrical and mechanical standpoints to generate the electron beams at such a pitch and modulate them individually. Even if it is possible, it is very difficult to keep the spot size of the electron beam constant and keep the incident position precision to the phosphor plane constant for all electron beams over an electron beam travel path between the electron gun and the phosphor plane. Since the voltage on the vertical deflection electrode switches from a voltage equal to that of the phosphor plane to a deflection voltage, switching takes place at a high voltage and a deflection power is fairly large.